Inhibition of yellowing in papers

ABSTRACT

Lignin-containing papers are rendered light stable when they contain TiO 2  in combination with an amine hindered radical scavenger.

TECHNICAL FIELD

[0001] The present invention relates to light stable lignin-containingpapers and to methods of rendering lignin-containing papers lightstable; more especially the invention provides a method that can be usedin paper mills to produce light stable lignin-containing papers by theapplication of titanium dioxide and a radical scavenger, which can beadded to the base paper sheet or as a component of pigment coatingformulations employed to coat the paper.

BACKGROUND ART

[0002] Numerous processes are known to convert various types of wood,recycled paper and other fibrous raw materials into pulp suitable formaking paper. In general, these processes can be categorized asmechanical pulping, chemical pulping and combinations thereof.

[0003] In mechanical pulping processes, such as the processes whichproduce refiner mechanical pulp (RMP) and thermomechanical pulp (TMP)processes, the fibres are separated by a combination of heat andmechanical force. Stone groundwood pulp (GWD) is produced by grindinglogs between heavy stones. Such processes produce pulps at a lower cost,at a yield of about 95%, by wt., based on starting wood.Chemithermo-mechanical pulp (CTMP) and chemimechanical pulp (CMP)processes apply some degree of chemical treatment to improve thestrength properties of the pulp. The yield is somewhat reduced by thechemical treatment, but it is still substantially higher, usuallygreater than 80%, by wt., than that from a purely chemical pulpingprocess. These high-yield mechanical pulps are bleached, if desired,with chemicals that do not remove lignin, such as hydrogen peroxide orsodium dithionite.

[0004] The traditional market of high-yield pulps is newsprint andshort-life advertising papers. However, there is intensive interest inusing bleached mechanical pulps in value-added paper grades. Paper madefrom mechanical pulp has attractive optical and printing properties.Advances in pulping and bleaching technology have made it possible toproduce high-yield pulps with suitable strength and brightness for usein high-value printing and writing grades of paper, which currently usebleached chemical pulp almost exclusively. However, rapid light-inducedyellowing of lignin in high-yield pulps remains a significant impedimentto their broader use. A. Cockram, (CTMP in Fine Papers., 1989International Mechanical Pulping Conference Proceedings, 1989,Helsinki., p. 20), estimated that, if the time taken for light-inducedyellowing of these papers could be increased by 3-36 months, thepotential market for bleached TMP and CTMP would be expanded by 0.6-2.2million tons per year.

[0005] Most of the discoloration is due to lignin, which undergoesphotochemical reactions that form coloured groups when exposed to nearultra-violet (UV) light (wavelength 300-400 nm). Many methods to inhibitthe yellowing of mechanical pulps have been attempted. These can begenerally classified into two main groups: blocking the yellowingreactions through lignin modification; and adding chemicals that eitherstop or redirect the photochemistry to avoid colored products. This hasbeen completely reviewed by C. Heitner in “Photochemistry ofLignocellulosic Materials”, C. Heitner, J. C. Scaiano, eds,:ACS Sym.Ser. 531, 1-25 (1993), and “Chemistry of Brightness Reversion and itsControl, Chapter 5”, Pulping Bleaching-Principles and Practice, C. W.Dence, D. W. Reeve, eds., Tappi Press, Atlanta, 1996, pp 183-211.International publication WO 99/05108 discloses that yellowinginhibitors based on hindered amines, nitroxides, hydroxylamines andalkoxyamines can be used together with an organic-based ultra violetabsorber (UVA) to give lignin-containing papers light stabilitycomparable to that found in papers made from lignin-free kraft pulps.However, the cost of the UVA is not trivial and may be difficult tojustify for printing and writing papers.

[0006] Pigmented coatings and fillers improve paper gloss, color, andprintability. They can also improve brightness stability, depending ontype and amount of the pigments used. The pigments provide somebrightness stability, either by scattering or absorbing incident UVlight. Clay and calcium carbonate provide brightness stability primarilyby the scattering mechanism, since they have a high reflectance but alow absorption of UV light.

[0007] Robert Johnson (CTMP in fine papers: on-machine surfacetreatments for improved brightness stability, Tappi Journal, May 1991,p. 209) examined the use of TiO₂ to improve the brightness stability ofpapers containing up to 50% CTMP. With 50% CTMP in the base sheet,brightness stability equivalent to wood-free papers was achieved whenthe sheet was coated at 14 g/m²/side with a formulation where 6% of thepigment was rutile TiO₂. Thin surface treatments or “lick coatings” (5g/m²/side), where 10% of the pigment is TiO₂ and the remainder is clayor CaCO₃, also improved the brightness stability, but not as much as thefully coated sheet (14 g/m²/side). The effect of TiO₂ on papers madefrom 100% mechanical pulps has not been examined.

DISCLOSURE OF THE INVENTION

[0008] The present invention provides a method that can be used toproduce light stable lignin-containing papers using TiO₂ pigment and aradical scavenger. Light stable lignin-containing papers or paperboardscan be produced with this method.

[0009] The invention also provides a light stable lignin-containingpaper containing TiO₂, and a radical scavenger.

[0010] In accordance with one aspect of the invention there is provideda light stable lignin-containing paper having a content of particulatetitanium dioxide and a radical scavenger effective to inhibit yellowingof the paper.

[0011] In accordance with another aspect of the invention there isprovided a method of rendering a lignin-containing paper light stablecomprising: a) incorporating in said paper a content of particulatetitanium dioxide and a radical scavenger, in an amount effective toinhibit yellowing of the paper, or b) coating the paper with a coatingformulation having a content of particulate titanium dioxide and aradical scavenger, in an amount effective to inhibit yellowing of thepaper.

DETAILED DESCRIPTION OF THE INVENTION AND DESCRIPTION OF PREFERREDEMBODIMENTS

[0012] Advances in printing and packaging technology are placing greaterdemands on paper quality, particularly optical and surface properties.

[0013] In this invention it is found that the combined use of titaniumdioxide and a radical scavenger in a lignin-containing paper sheet or ina coating on a lignin-containing paper sheet, inhibits yellowing of thepaper sheet, and more especially produces an inhibiting effect greaterthan the summation of the individual effects of the titanium dioxide andthe radical scavenger.

[0014] i) Paper

[0015] The lignin-containing papers of the invention, are papers of highlignin content in which yellowing occurs as a result of modifications inthe lignin in the paper.

[0016] More especially these are papers derived from pulp having as amajor component a high yield pulp produced in mechanical pulpingprocesses, more especially stone groundwood pulp, refiner mechanicalpulp, thermomechanical pulp, chemithermomechanical pulp andchemimechanical pulp, which are produced in yields greater than 80%, bywt. High yield indicates high retention of lignin and these pulpstypically have a lignin content (Klason lignin) of 15 to 35%, by weight,based on the weight of the pulp. Lignin content varies as betweenhardwoods and softwoods and between species. In general these pulpsderived from hardwoods have a lignin content of 15-25%, by weight, ofthe pulp and the pulps derived from softwoods have a lignin content of20 to 35%, by weight of the pulp.

[0017] Typically the pulp will be bleached, for example, with peroxide,the bleaching does not remove the lignin.

[0018] The paper may be formed from such bleached high yield pulp as thesole pulp component or the bleached high yield pulp may be co-mixed witha chemical pulp, for example, kraft pulp.

[0019] In general, the high yield pulp will comprise more than 10%, byweight, and preferably more than 50%, more preferably 80% to 100%, byweight, of the pulp component of the paper.

[0020] ii) TiO₂:

[0021] TiO₂ is the most efficient light-scattering pigment commerciallyavailable, due to its high refractive index. Thus, it is known in theart that TiO₂ can be used as a filler, usually together with otherpigments such as clay or ground or precipitated calcium carbonate, toimprove optical properties such as brightness and opacity.

[0022] Pigmented coatings, in addition to enhancing optical properties,improve surface properties such as gloss, smoothness, color, printingdetail, and brilliance. The TiO₂ may also be employed in pigmentedcoatings together with clay, calcium carbonate and other pigments. Suchcoatings can be applied on or off machine with various kinds ofequipment including, but not restricted to, blade, rod or airknifecoaters, or film coating size presses. Surface application of chemicalsand pigments provides close to 100% retention, which reduces wet-enddeposits, wear of paper machine clothing and effluent loads.

[0023] In addition to its superlative scattering properties, TiO₂ is astrong absorber of near UV light. Thus, TiO₂ can stabilize paperbrightness by both scattering and absorbing UV light.

[0024] TiO₂ occurs in rutile and anatase crystal forms. While both formshave high scattering power and high near UV absorption, the Futile formis preferred in this invention. The rutile form is more stable withregard to outgassing and has a higher near UV absorption.

[0025] The behaviour of TiO₂ is strongly influenced by its averageparticle size. The current invention exploits both UV absorbing andscattering properties of TiO₂. Particle sizes from 0.01 to 1.5 micronsare typically employed. Particle sizes ranging from 0.1 to 1.5 micronsare preferred due to their better scattering ability, and within thisrange, particle sizes from 0.16 to 0.28 microns are even more preferred.

[0026] The TiO₂ is suitably employed in the paper in an amount of 0.05to 10%, preferably 0.5 to 15% and more preferably 1 to 10%, by weightbased on the oven dry weight of fibre.

[0027] iii) Radical Scavengers:

[0028] Radical scavengers are used in conjunction with the TiO₂ eitherin the base sheet or in a coating, to improve the brightness stabilityof the lignin-containing papers. Both agents show better brightnessstability as dosages are increased up to a limiting value. In accordancewith the invention it has been found that combining these two agentsprovides better brightness stability than is possible using either agentalone.

[0029] Thiols, ascorbate and hindered amine compounds are radicalscavengers that have some efficacy at reducing light-induced yellowing.

[0030] The hindered amine compounds such as described by Seltzer et al.,McGarry et al. and Yuan et al. are preferred because of their superiorthermal stability and lack of objectionable odor. (Seltzer et al(International publication WO 99/05108) McGarry et al, (J. Pulp PaperSci., (2000), 26(2), 59-66) and Yuan et al (Proceedings: PAPTAC 87thAnnual Meeting, Montreal, 2001, (PAPTAC) C43-C52).

[0031] In typical papermaking practice, pigments comprise as much as40%, by weight, of total mass of the paper when used as a filler, and upto 50%, by weight, when applied as a coating. It is technically possibleto use TiO₂ as the only pigment. However, preferred methods use TiO₂loadings of 0.05% to 50%, more preferably 2 to 30%, by weight of thetotal pigments. Suitable pigments for use with TiO₂ in the filler orcoating include but are not restricted to clay and ground orprecipitated calcium carbonate, as extenders.

[0032] It is known in the art that hindered amine radical scavengersimprove the brightness stability of lignin-containing papers. Thesecompounds are exemplified by the piperidine and pyrrolidine structures Athrough D:

[0033] in which:

[0034] R₁ is selected from hydrogen, hydroxyl, primary, secondary,tertiary or quaternary amino, alkyl, alkoxy, aminoalkyl alkylene oxideof the general formula [—O—(CH2)_(n)]_(N) where n is 1 to 4 and N is 1to 20. The alkyl or alkyl moiety in R₁ has from 1 to 12 carbons, and maybe straight chain or branched. The alkyl and alkyl moieties may beunsubstituted or substituted with hydroxyl (OH), carboxyl (COOH) orcarboxylate (COO⁻ _(r)M_(r/z) ^(x+)) groups with M being a metal ionfrom the 1st, 2nd or 3rd group of the periodic table, or Zn, Cu, Ni orCo; or M is a group N⁺(R₆)₄ where R₆ is alkyl of 1 to 8 carbon atoms orberizyl, and r and z are each integers of 1, 2 or 3;

[0035] R₂ and R₃ can be the same or different and are selected fromhydrogen, hydroxyl (OH), carboxyl (COOH) or carboxylate (COO⁻_(r)M_(r/z) ^(z+)) groups with M being a metal ion from the 1st, 2nd or3rd group of the periodic table, or Zn, Cu, Ni or Co; or M is a groupN⁺(R₆)₄ where R₆ is alkyl of 1 to 8 carbon atoms or benzyl, and r and zare each integers of 1, 2 or 3;

[0036] Y is oxyl or hydroxyl; and

[0037] X is an inorganic or organic anion, such as carbonate, borates,bicarbonate, chloride, bisulfate, sulfate, formate, acetate, citrate,oxalate, ascorbate, phosphonate, phosphate, nitrate, bromide, bisulfite,sulfite, benzoate, tartrate, acrylate, polyacrylate, fumarate, maleate,itaconate, glycolate, gluconate, malate, mandelate, tiglate,polymethacrylate, a carboxylate of nitrilotriacetic acid,hydroxyethylethylenediaminetriacetic acid, ethylenediaminetetraaceticacid or of diethylenetriaminepentaacetic acid, adiethylenetriaminepentamethylenephosphonate, an alkylsulfonate or anarylsulfonate and p is an integer of 1 to 20, preferably 1 to 10, morepreferably 1 to 5 and most preferably 1, 2 or 3 and m is an integer of 1to 20, preferably 1 to 10, more preferably 1 to 5 and most preferably 1,2 or 3, typically m and p may be integers 1, 2 or 3.

[0038] The hindered amine radical scavenger is suitably employed in anamount of 0.05 to 5%, preferably 0.1 to 2% and more preferably 0.1 to1.0%, by weight, based on the weight of oven dried fibres.

[0039] iv) Organic Ultra Violet Absorber:

[0040] In preferred embodiments, an organic ultra violet absorber (UVA),for example, o-hydroxybenzophenone or o-hydroxyphenylbenzotriazole isemployed in addition to the titanium dioxide and the radical scavengerand this is found to further inhibit yellowing.

[0041] The UVA is suitably employed in an amount of 0.1 to 0.8%,preferably 0.1 to 0.4%, by wt. based on the weight of oven dry fibres.

BRIEF DESCRIPTION OF DRAWINGS

[0042]FIG. 1 is a plot demonstrating the relationship between the PCnumber and the content of TiO₂, at different coating weights;

[0043]FIG. 2 is a plot demonstrating the relationship between PC numberand content of TiO₂ at different contents of radical scavenger;

[0044]FIG. 3 is a plot demonstrating the relationship between PC numberand content of radical scavenger at different contents of TiO₂;

[0045]FIG. 4 is a plot demonstrating the relationship between PC numberand content of TiO₂ at a fixed content of radical scavenger;

[0046]FIG. 5 is a plot demonstrating the relationship between PC numberand accelerated exposure to light for different contents of TiO₂ andTiO₂ in combination with a radical scavenger in a coating; and

[0047]FIG. 6 is a plot similar to FIG. 5 but employing the TiO₂ asfiller rather than in a coating.

EXAMPLES

[0048] The present invention will be illustrated by the followingexamples. Machine-made papers containing mechanical pulp were coatedwith pigmented formulations with or without TiO₂ or a radical scavenger(RS). The citric acid salt of4-hydroxy-2,2,6,6-tetramethyl-N-hydroxypiperidine was used as theradical scavenger. Rutile TiO₂ slurry was used in the experiments. Twodifferent coating formulations were used. The effect of RS on theyellowing inhibition was tested by incorporating the inhibitor as anadditive in the formulation. The effect of TiO₂ was examined bysubstituting it for a portion of the calcium carbonate in the coatingformulations.

[0049] Accelerated photolysis was done in an exposure chamber equippedwith cool-white fluorescent lamps. The light intensity in the chamberwas approximately 50 times that of normal office light. ISO brightnesswas determined according to ISO standard 2470, using a Technidyne MicroTB-1C reflectometer. The light stability of the paper is presented bythe change in either ISO brightness or PC number as a function ofaccelerated irradiation time. The brightness data were converted topost-color number (PC number) according to the following two equations:

PC=((k/s)_(after)−(k/s)_(before))×100  (1)

k/s=(1−R _(∞))²/2R _(∞)  (2)

[0050] Where k and s are the absorption and scattering coefficients ofthe paper, respectively, and R_(∞) is the ISO brightness expressed as afractional value. To a rough approximation, PC number is directlyproportional to the chromophores formed during light-induced yellowing.Therefore the smaller the PC number, the less the paper has yellowed.

[0051] The % of TiO₂, RS and UVA is by weight based on the weight ofoven dried fibres.

Example 1

[0052] A 49 g/m² base paper, with an initial brightness of 72%, wascoated with various amounts of a pigmented coating color using a bladecylindrical laboratory coater (CLC). The base sheet contained in wt. %,97% alkaline peroxide bleached mechanical pulp (APMP) pulp and 3% kraftpulp. The pigmented coating color contained, in wt. %, 55% clay, 45%ground calcium carbonate, starch, latex, and coating additives. Theinitial ISO brightness varied from 74.5% to 81.0% depending on the totalcoat weight and amount of TiO₂ incorporated in the coating.

[0053]FIG. 1 plots the PC number obtained after 12 days acceleratedexposure as a function of TiO₂ content for coat weights of 4, 9 and 14g/m²/side. These weights correspond approximately to light, medium andheavy coating. The different values of the intercepts for each line showthat the clay/calcium carbonate coating itself, in the absence of TiO₂,affords some inhibition of yellowing, and that this inhibition improveswith increasing coat weight. Adding TiO₂ at any coat weight furtherimproves the yellowing inhibition. Inhibition improves with increasingTiO₂ addition up to a maximum between 5% to 6% on fiber. Althoughyellowing slows, it still occurs at these maximum levels of TiO₂.

Example 2

[0054] A coated paper as described in Example 1 was prepared with a 9g/m²/side coat weight. Samples containing TiO₂ and the citric acid saltof 4-hydroxy-2,2,6,6-tetramethyl-N-hydroxypiperidine as radicalscavenger were tested for light stability.

[0055]FIG. 2 shows the resulting plot of PC number after 12 daysaccelerated exposure versus the amount of TiO₂ added. As noted inExample 1, when TiO₂ alone is used, yellowing inhibition is maximized ata TiO₂ content between 5% and 6%. FIG. 2 also shows that adding radicalscavenger to a coating color containing TiO₂ enhances the yellowinginhibition. FIG. 2 also shows that adding radical scavenger to thecoating color improves yellowing inhibition under conditions where noadditional benefit can be obtained by increasing the amount of TiO₂.

[0056]FIG. 3 shows plots of PC number after 12 days exposure versus theamount of radical scavenger in the coating, at a coating weight of 9g/m² and different contents of TiO₂. The yellowing inhibition achievedby adding radical scavenger alone reaches a maximum at an application ofabout 0.5%/side. This maximum level can be improved by including TiO₂ inthe coating.

Example 3

[0057] Coated paper as described in Example 1 was prepared with a 14g/m²/side coat weight containing 0.3% of the radical scavenger4-hydroxy-2,2,6,6-tetramethyl-N-hydroxypiperidine citrate and variousamounts of TiO₂.

[0058] The plot in FIG. 4 shows that complete inhibition of yellowingafter 12 days accelerated exposure was possible using 0.3% of theradical scavenger with 3.5% TiO₂.

Example 4

[0059] A 57 g/m² machine-made paper made from 100% peroxide-bleachedsoftwood thermomechanical pulp, initial ISO brightness 78%, was treatedwith a pigmented formulation by a laboratory film applicator. The coatweight was 4 g/m² per side. The pigmented formulation consisted of 80%ground calcium carbonate and 20% delaminated clay, starch, latex, andsome minor additives. As shown in FIG. 5, replacing 12% of the CaCO₃with TiO₂ which corresponds to 1.15% TiO₂ charge on fiber, increased thebrightness stability. Doubling the amount of TiO₂ to 2.3% provided nofurther improvement in brightness stability. Adding 1.0% of the radicalscavenger together with 1.15% TiO₂ gave a brightness stability betterthan that possible using TiO₂ alone.

Example 5

[0060] A paper made from a 57 g/m² base sheet with a 4 g/m² coating, asdescribed in Example 4, was prepared. In addition to the control,samples containing 0.6% TiO₂, 1% radical scavenger and both 0.6% TiO₂and 1% radical scavenger were irradiated for 12 days. The PC numbervalues are listed in Table 1. The data show that the effect of addingTiO₂ and radical scavenger together at the indicated levels (smallerincrease in PC number) is greater than the sum of their individualeffects. TABLE 1 Change in PC Number for BTMP paper with 4g/m²/sidecoating Sum of individual effects of adding TiO₂and radical scavengerEffect of adding TiO₂ and radical (PC_(control)-PC_(TiO2)) +(PC_(control)- scavenger together Sample PC number PC_(RS))PC_(control)- PC_(TiO2+RS) Control 16.92 0.6% TiO₂ 14.80 7.69 9.58 1% RS11.35 0.6% TiO₂ + 7.34 1% RS

Example 6

[0061] Coated paper using a 49 g/m² base sheet and 9 g/m²/side coatingwere prepared as described in Example 1. Samples were preparedcontaining the following yellowing inhibitors in the coating colour:control (no inhibitor), 1.5% TiO₂ plus 0.4% radical scavenger and 0.3%organic UVA (a 60/40 mixture of hydroxyphenylbenzotriazole structures Eand F below, where n=5-9), 1.5% TiO₂ plus 0.4% radical scavenger and0.3% organic UVA.

[0062] The PC number values after 12 days of accelerated exposure aretabulated in Table 2. The data show that the effect (smaller increase inPC number) of adding TiO₂, radical scavenger, and organic UVA togetherat the indicated levels is greater than the sum of the individualeffects of radical scavenger +organic UVA and TiO₂. TABLE 2 Change in PCNumber for mechanical paper with 9 g/m²/side coating Sum of individualeffects of Effect of adding TiO₂ number adding TiO₂ and radical andradical scavenger scavenger together PC (PC_(control)-PC_(TiO2)) +PC_(control) - Sample Number (PC_(control)-PC_(RS+UVA)) PC_(TiO2+RS+UVA)Control 6.06 1.5% TiO₂ 5.81 2.79 3.26 0.4% RS + 3.52 0.3% UVA 1.5%TiO₂ + 2.8 0.4% RS + 0.3% UVA

Example 7

[0063] A 100 g/m² standard handsheet made from 100% peroxide-bleachedsoftwood thermomechanical pulp, initial brightness 73%, was preparedeither with or without rutile TiO₂ as filler. The TiO₂ retained in thesheets was 13.7% based on o.d. fiber. The control and filled sheets werealso treated with 1.0% radical scavenger by a laboratory filmapplicator. As shown in FIG. 6, like surface treatment, TiO₂ alsoimproved the paper brightness stability when it was retained in thesheet as filler. The radical scavenger improved the paper brightnessstability, but a combination of TiO₂ and radical scavenger offered muchbetter yellowing inhibition.

1. A light stable lignin-containing paper having a content ofparticulate titanium dioxide and a radical scavenger effective toinhibit yellowing of the paper.
 2. A paper according to claim 1, whereinsaid radical scavenger is a hindered amine radical scavenger. 3.(Amended) A paper according to claim 1, wherein said titanium dioxide isrutile titanium dioxide having a particle size of 0.01 to 1.5 micronsand is present in an amount of 0.05 to 10%, by weight, based on theweight of oven dry pulp fibre in the paper.
 4. A paper according toclaim 3, wherein said titanium dioxide is in an amount of 0.5 to 6%, byweight, based on the weight of oven dry pulp fiber and said particlesize is 0.1 to 1.5 microns.
 5. A paper according to claim 3, whereinsaid titanium dioxide is in an amount of 1 to 5%, by weight, based onthe weight of oven dry fibre and said particle size is 0.16 to 0.28microns.
 6. (Amended) A paper according to claim 1, wherein said radicalscavenger is present in an amount of 0.05 to 5%, by weight, based on theweight of oven dry fibre.
 7. (Amended) A paper according to claim 1,wherein said radical scavenger is present in an amount of 0.1 to 2%, byweight, based on the weight of oven dry fibre.
 8. (Amended) A paperaccording to claim 1, wherein said radical scavenger is present in anamount of 0.1 to 1.0%, by weight, based on the weight of oven dry fibre.9. (Amended) A paper according to claim 1, wherein said radicalscavenger is selected from piperidines and pyrolidines of formula A, B,C and D:

in which: R₁ is selected from hydrogen, hydroxyl, primary, secondary,tertiary or quaternary amino, alkyl, alkoxy, aminoalkyl alkylene oxideof the general formula [—O—(CH2)_(n)]_(N) where n is 1 to 4 and N is 1to
 20. The alkyl or alkyl moiety in R₁ has from 1 to 12 carbons, and maybe straight chain or branched. The alkyl and alkyl moieties may beunsubstituted or substituted with hydroxyl (OH), carboxyl (COOH) orcarboxylate (COO⁻ _(r)M_(r/z) ^(z+)) groups with M being a metal ionfrom the 1st, 2nd or 3rd group of the periodic table, or Zn, Cu, Ni orCo; or M is N⁺(R₆)₄ where R₆ is alkyl of 1 to 8 carbon atoms or benzyl;and r and z are each integers of 1, 2 or 3; R₂ and R₃ can be the same ordifferent and are selected from hydrogen, hydroxyl (OH), carboxyl (COOH)or carboxylate (COO⁻ _(r)M_(r/z) ^(z+)) groups with M being a metal ionfrom the 1st, 2nd or 3rd group of the periodic table, or Zn, Cu, Ni orCo; or M is a group N⁺(R₆)₄ where R₆ is alkyl of 1 to 8 carbon atoms orbenzyl, and r and z are each integers of 1, 2 or 3; Y is oxyl orhydroxyl; and X is an inorganic or organic anion, p and m are integersof 1 to
 20. 10. (Amended) A paper according to claim 1, wherein saidtitanium dioxide and radical scavenger are present with filler in thepaper.
 11. (Amended) A paper according to claim 1, wherein said titaniumdioxide and said radical scavenger are present in a pigment coating onat least one side of the paper.
 12. (Amended) A paper according to claim1, further including an organic ultra violet absorber with said titaniumdioxide and radical scavenger.
 13. (Amended) A paper according to claim1, derived from a lignin-containing pulp having a lignin content of 15to 35%, by weight, based on the weight of oven dry fibre lignin in thelignin-containing pulp.
 14. (Amended) A paper according to claim 1,derived from a pulp which comprises a high yield pulp selected fromrefiner mechanical pulp, stone groundwood pulp, thermomechanical pulp,chemithermo-mechanical pulp and chemimechanical pulp in an amount of 80to 100%, by weight, based on the total pulp weight.
 15. A method ofrendering a lignin-containing paper light stable comprising: a)incorporating in said paper a content of particulate titanium dioxideand a radical scavenger, in an amount effective to inhibit yellowing ofthe paper, or b) coating the paper with a coating formulation having acontent of particulate titanium dioxide and a radical scavenger, in anamount effective to inhibit yellowing of the paper.
 16. A methodaccording to claim 15, wherein said radical scavenger is a hinderedamine.
 17. (Amended) A method according to claim 15, wherein saidtitanium dioxide is rutile titanium dioxide having a particle size of0.01 to 1.5 microns and is present in an amount of 0.05 to 10%, byweight, based on the weight of oven dry pulp fiber in the paper.
 18. Amethod according to claim 17, wherein said titanium dioxide is in anamount of 0.5 to 6%, by weight, based on the weight of oven dry pulpfiber.
 19. A method according to claim 17, wherein said titanium dioxideis in an amount of 1 to 5%, by weight, based on the weight of oven dryfibre and said particle size is 0.16 to 0.28 microns.
 20. (Amended) Amethod according to claim 15, wherein said radical scavenger is presentin an amount of 0.05 to 5%, by weight, based on the weight of oven dryfibre.
 21. (Amended) A method according to claim 15, wherein saidradical scavenger is present in an amount of 0.1 to 1.0%, by weight,based on the weight of oven dry fibre.
 22. (Amended) A method accordingto claim 15, wherein said radical scavenger is selected from piperidinesand pyrrolidines of formula A, B, C and D:

in which: R₁ is selected from hydrogen, hydroxyl, primary, secondary,tertiary or quaternary amino, alkyl, alkoxy, aminoalkyl alkylene oxideof the general formula [—O—(CH2)_(n)]_(N) where n is 1 to 4 and N is 1to
 20. The alkyl or alkyl moiety in R₁ has from 1 to 12 carbons, and maybe straight chain or branched. The alkyl and alkyl moieties may beunsubstituted or substituted with hydroxyl (OH), carboxyl (COOH) orcarboxylate (COO⁻ _(r)M_(r/z) ^(z+)) groups with M being a metal ionfrom the 1st, 2nd or 3rd group of the periodic table, or Zn, Cu, Ni orCo; or M is N⁺(R₆)₄ where R₆ is alkyl of 1 to 8 carbon atoms or benzyl;and r and z are each integers of 1, 2 or 3; R₂ and R₃ can be the same ordifferent and are selected from hydrogen, hydroxyl (OH), carboxyl (COOH)or carboxylate (COO⁻ _(r)M_(r/z) ^(z+)) groups with M being a metal ionfrom the 1st, 2nd or 3rd group of the periodic table, or Zn, Cu, Ni orCo; or M is a group N⁺(R₆)₄ where R₆ is alkyl of 1 to 8 carbon atoms orbenzyl, and r and z are each integers of 1, 2 or 3; Y is oxyl orhydroxyl; and X is an inorganic or organic anion, p and m are integersof 1 to
 20. 23. (Amended) A method according to claim 15, wherein saidtitanium dioxide and scavenger are incorporated with filler in the paperin accordance with a).
 24. (Amended) A method according to claim 15,wherein said titanium dioxide and said radical scavenger are present insaid coating formulation in accordance with b).
 25. (Amended) A methodaccording to claim 15, further including an organic ultraviolet absorberwith said titanium dioxide and radical scavenger.
 26. (Amended) A methodaccording to claim 15, wherein said paper is derived from alignin-containing pulp having a lignin content of 15 to 35%, by weight,based on the weight of oven dry fibre lignin in the lignin-containingpulp.
 27. (Amended) A method according to claim 15, wherein said paperis derived from a pulp which comprises a high yield pulp selected fromrefiner mechanical pulp, stone groundwood pulp, thermomechanical pulp,chemithermomechanical pulp and chemimechanical pulp in an amount of atleast 10%, by weight, based on the total pulp weight.
 28. (Cancel) Useof particulate titanium dioxide in conjunction with a radical scavengerin a lignin-containing paper to inhibit yellowing.
 29. (Cancel) Useaccording to claim 28, wherein said radical scavenger is a hinderedamine radical scavenger.